Prior art patent document published CH 239079 discloses a closing member in the form of a mushroom, i.e. comprising an elongate portion and a shoulder portion around the elongate portion. A rubber seal packing is formed around the elongate portion and on the shoulder portion and is then vulcanised so as to properly adhere to the body of the closing member. The problem of rubber deformation and/or extrusion due to high and/or repetitive loads is neither addressed nor resolved in this teaching.
Prior art patent document published BE 716804 addresses the problem of deterioration of the rubber of a closing member of the type of the preceding document by providing one or several ring shaped slots on the lateral surface of the rubber. This or these slots are intended to reduce the shearing forces exerted by the sharp edge of the shoulder portion of the body of the closing member on the elastomer material. These measures do not however solve the problem of permanent deformation or matting of the rubber at its contact surface with a valve seat.
The prior art patent document published GB 908 919 discloses a valve device of the type of a water cock where the closing member comprises an elongate portion, a shoulder portion and a skirt or sleeve integral with the shoulder and forming an annular cavity receiving an annular elastomeric seal. The seal is surrounded by a sleeve slidable within the cavity. Additionally, the cavity has in its bottom face an annular recess in front of a bevelled corner of the seal so as to allow the elastomeric material to deform and move into the recess thereby increasing its effective resilience. This construction is however essentially directed to manually-operated shut-off valves, i.e. valves where the closing effort is manually exerted by means of a screw mechanism. It is intended to solve the problem of water cocks where the limited resilience of the seal has for effect after having shut-off a hot-water cock that a leakage can occur when the seal cools down. This construction is therefore not adequate for spring biased shut-off valves.
Prior art patent document GB 875 446 discloses a water cock where the closing member comprises an elastomeric seal disposed on a shoulder portion and on which a sleeve is slid and crimped. Both the closing member body and the sleeve have each a ridge from which elastomeric material slightly protrude. The ridges are intended to come into contact with the seat when the valve in shut-off by a manual operation. The limited amount of elastomeric material protruding from the ridges is intended to provide an elastic contact with the seat whereas the ridges are intended to limit this elastic contact. The construction discloses in this document is clearly conceived from manually operated valves like a water cock.